System runs real-time control over Etherenet

PowerDNA (which refers to distributed, networked automation and control) is a system that sets new benchmarks for hard real-time I/O using standard Ethernet cabling.

PowerDNA (which refers to distributed, networked automation and control) is a system that sets new benchmarks for hard real-time I/O using standard Ethernet cabling.

Developed by United Electronic Industries, the modular system is optimised for real-time control applications requiring both large numbers of analogue and digital I/O points as well as extremely fast response.

Thanks to the patent-pending DaqBIOS protocol, which transfers commands and data over Ethernet hardware in a deterministic fashion, a PowerDNA system consisting of a PCI/PXI-based controller and multiple distributed nodes with more than 800 mixed analogue and digital I/O points can guarantee a response in better than 1ms.

A wide selection of I/O configurations is available from the factory.

"We have listened to the voice of the customer and have developed PowerDNA, which meets the needs for distributed hard real-time I/O for the next decade", comments Shaun Miller, president of UEI.

"For several years engineers could purchase Ethernet-based I/O but with insufficient real-time response to address future system requirements.

However, the development of the PowerDNA DaqBIOS protocol has solved this problem".

At the highest level, PowerDNA consists of a central controller card that fits into a host PC or PXI/CompactPCI system, and it supplies either one, two or four Ethernet ports.

To each of these ports, users can attach as many as 64 I/O cubes.

Each I/O cube in turn consists of a metal enclosure that contains a communications layer, a CPU layer with an embedded real-time kernel, and positions for either three or six I/O layers.

Customers select the desired functionality from a range of I/O layers, which are factory installed, configured and calibrated.

Users program their applications in C using a straightforward API that provides access to all hardware functionality.

After compiling an application on the host PC, engineers can download it to an I/O Cube in several ways: over the Ethernet, over a serial link, over a USB port or even with a PDA equipped with an infra-red link.

The application can run under host control or as a stand-alone task.

The central controller resides in a PC or PXI/CompactPCI system, and it is equipped with a 333MHz PowerPC processor, 128Mbyte of RAM and 64Mbyte of CompactFlash memory that stores programs and a mini-OS.

The controller offers from one to four 100BaseT network interfaces, each of which can control as many as 64 I/O modules.

The controllers can run the high-performance DaqBIOS protocol, but they also support standard protocols such as TCP/IP that allow users to integrate factory-floor tasks with an enterprise system.

As for software, the central controller executes QNX, real-time Linux or VXWorks.

And even when supporting hard real-time operation, 80% of the processor's time is available to run a user application.

Each I/O cube starts with a CPU layer, which contains a ColdFire CPU running at 66MHz plus 16Mbyte of SDRAM and 4Mbyte of Flash memory.

This layer also provides an IrDA interface so users can field-configure the CPU module with the assistance of any infra-red-equipped PDA.

Next, the I/O cube also comes with the network layer, which provides two RJ45 jacks for daisychaining the Ethernet link to other I/O cubes; it also provides a USB port and a serial port over which users can download new programs or upload process data.

Users can also daisychain power from cube to cube within this layer.

The small unit also holds as many as six I/O layers, each connecting to the CPU layer over a 32bit 33MHz bus with optoisolation so errant field signals cannot disrupt system operation.

A five-layer I/O cube with room for three I/O layers measures 4 x 4 x 4in, whereas the eight-layer version is 6 x 4 x 4in.

When configuring an I/O cube, users can select from several I/O layers: analogue input (16 channels, 16bit resolution, 100Ksample/s digitisation rate); analogue output (eight channels, 16bit resolution, 100Ksample/s update rate); temperature measurement (24 channels, 24bit A/D, direct sensor connection); digital I/O (with either eight or 16 bidirectional lines); communication (eight RS232/485 ports); and four-axis motion control.

Soon to be available are layers that supply mass storage and battery operation, making the unit ideal for stand-alone data logging or remote/vehicular operation.

The central controller communicates through the I/O cube's network layer to individual I/O layers using the patent-pending DaqBIOS protocol.

It employs either isosynchronous operation with time-sharing, or variable timing in a broadcast scheme, or both.

Because the protocol is optimised for process applications, the overhead per message is extremely low and the scheme achieves impressive response times.

For example, in a system with 16 modules (3072 I/O points) using variable timing, the time required to communicate with all I/Os is less than 1ms.

The DNA-CC central controller starts at GBP 1750 with one communications port; and an I/O cube with the network and CPU layers along with three open I/O-layer positions costs GBP 575; an I/O cube with six open I/O layers sells for GBP 675.

The I/O layers themselves range from GBP 260 (eight-channel analogue output) to GBP 1170 (four-axis motion control).

(This was Engineeringtalk's Top Story on 30 September 2002).

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